This application claims priority from Japanese patent application 325529/2001, filed in Japan on Oct. 23, 2001.
This invention relates to a plastic movable guide for a power transmission in which an endless chain transmits power from a driving sprocket to a driven sprocket or an endless belt transmits power from a driving pulley to a driven pulley. The guide may be used, for example, as a fixed guide, or as a pivotally mounted tensioner lever.
Many engines, and other machines in which mechanical power is transmitted from one shaft to another, include a circulating transmission device, comprising a chain, a belt, or the like as shown in FIG. 10. A movable guide Ga, on which the transmission medium C slides, may be used, in cooperation with a tensioner T, to impart appropriate tension to the transmission medium, and also to prevent vibration in the plane of circulation of the transmission medium and also transverse vibration. The movable guide Ga is ordinarily attached to a frame E of the engine or other machine by a supporting shaft P, which may be a mounting bolt, a pin, or the like. In FIG. 10, an endless, circulating transmission medium is engaged with a driving sprocket S1, driven sprockets S2, and a fixed guide Gb for guiding, and limiting the traveling path of, the circulating transmitting medium C.
FIGS. 8 and 9 show a plastic movable guide 300, used as a tensioner lever in a transmission device utilizing a chain, as described in present inventors"" previously filed Japanese Patent Application No. 2000-382798.
In this plastic movable guide 300, a guide body 301 includes a shoe 302. A transmitting medium C, such as a traveling chain, belt or the like, is in sliding contact with a surface of the shoe. A plate-receiving portion 303, provided on the back of the shoe 302, and extending along the longitudinal direction of the guide, is molded of synthetic resin as a unit with the shoe. A reinforcing plate 308, composed of a rigid material which reinforces the guide body 301, fits into a slot 307, which opens in an edge of the plate-receiving portion 303 along the longitudinal direction of the guide, and faces in a direction opposite to the direction in which the chain-engaging surface of the shoe faces. A mounting hole 305, for mounting on the frame of an engine, or other machine, is provided at a fixed end of the plate-receiving portion 303. A through hole 308A is also provided at one end of the reinforcing plate 308. The through hole is positioned and fastened, together with the mounting hole 305 in the guide body 301, on a shaft such as a mounting bolt or the like, with the reinforcing plate 308 fitting into the slot 307.
In the above-described plastic movable guide 300, the shoe 302 and the plate-receiving portion 303 are integrally molded as a unit from a synthetic resin. The guide body 301 itself performs a sliding function, and it is not necessary to provide a separate shoe member. Therefore, the number of the parts and the number of production steps is minimized. Furthermore, since a slot 307 opens at an edge of the plate-receiving portion 303 in the guide body 301 along the longitudinal direction of the guide, and the reinforcing plate 308 fits into the slot 307, the strength of the plastic movable guide in the pivoting direction is increased, and its bending rigidity, toughness, strength are significantly improved.
A mounting hole, for mounting the guide on a frame of an engine, a drive, or the like, is provided adjacent a fixed end of the guide body, and a through hole, which is positioned in register with the mounting hole of guide body, is provided adjacent one end of the reinforcing plate, so that the guide body and reinforcing plate can be fastened together on a supporting shaft, such as a mounting bolt, pin, or the like, which extends through both holes. Thus, both the guide body and the reinforcing plate can be pivotally rotated about a mounting axis while cooperating with each other without the reinforcing plate becoming disassembled from the guide body. Furthermore, since the reinforcing plate is only connected to the guide body by the supporting shaft adjacent one end of the reinforcing plate, and fits into the slot of the guide body, even if there is a difference between the coefficients of thermal expansion of the guide body and the reinforcing plate, the reinforcing plate and guide body are free to move relative to each other in the longitudinal direction of the guide, and thermal shape deformation and resulting breakage are avoided.
In the conventional plastic movable guide 300, the relationships between the respective sizes and shapes of the mounting hole 305 bored in the guide body 301 and the through hole 308A bored in the reinforcing plate 308, are not considered, and the diameter of the mounting hole 305 is set to be the same as that of the through hole 308A by design. However, a variation in working accuracy in production, and a difference between the coefficients of thermal expansion of the materials made the diameter of the hole 308A in the reinforcing plate smaller than the diameter of the hole 305 in the guide body, causing the edge of the through hole 308A to protrude inward past the inner periphery of the hole 305.
When the conventional plastic movable guide is attached to the frame of an engine and used as a tensioner lever, objectionable metallic noise and transverse vibration are generated, both exceeding the noise and vibration generated when a plastic movable guide composed only of resin was used. A solution to these problems is desirable in view of requirements for reduced engine noise.
Furthermore, in the conventional plastic movable guide, the reinforcing plate can seize on its supporting shaft due to friction. Friction between the reinforcing plate and its supporting shaft can also cause wear, generating metal powder, the presence of which inside an engine can lead to engine failure. Thus, it has been necessary to subject the reinforcing plate to a preliminary strengthening process such as heat treatment in order to enhance its wear resistance. The necessity of preliminary treatment results in an increase in production cost. Furthermore, subjecting the reinforcing plate to a strengthening process such as heat treatment or the like, causes distortion of the reinforcing plate, impairing the ability of the reinforcing plate to fit easily into the slot of the guide body, and potentially reducing assembly efficiency. Thus, improvements are also desirable to avoid seizing, wear, increased production cost and reduced efficiency of assembly.
The inventors have studied and analyzed the causes of metallic noise generation, transverse vibration, wear of the reinforcing plate and seizing of the plate on its supporting shaft. As a result of their studies, the inventors have unexpectedly found that these problems do not occur in all plastic movable guides, but occur only where the diameter of the through hole bored in the reinforcing plate is smaller than that of the mounting hole bored in the guide body, or in where a part of the inner periphery of the through hole in the reinforcing plate protrudes inwardly past the inner periphery of the mounting hole in the guide body. Thus, the inventors have determined that the above-mentioned problems result from direct contact between the support shaft, that is the mounting bolt, pin, or the like, and the inner periphery of the through hole bored in the reinforcing plate.
Accordingly, the objects of the invention are to solve the above-mentioned problems encountered in the production and use of prior art plastic movable guides, and to provide a plastic movable guide having excellent quietness, improved assembly efficiency, and reduced production cost.
The guide in accordance with the invention comprises an elongated guide body composed of an elongated shoe having a front surface for sliding contact with a power transmission medium and a back side. A plate-receiving portion extends longitudinally along the back side of the shoe and has a longitudinally extending slot open in a direction opposite to the direction in which the front surface of the shoe faces. The shoe and plate-receiving portion are integrally molded as a unit from a synthetic resin. A reinforcing plate fits into the slot.
The guide body has a mounting hole adjacent one end thereof, and the reinforcing plate has a through hole adjacent one of its ends. When the reinforcing plate is seated in the slot, the elongated mounting hole and the through hole are substantially coaxial with each other so that an attachment means, inserted through the mounting and through holes, can support the guide body and reinforcing plate on a frame of an engine. The structure is characterized by the fact that the diameter of the through hole in the reinforcing plate is greater than the diameter of the mounting hole in the guide body.
In a preferred embodiment, a locking means is provided for positioning and locking the through hole and the mounting hole in coaxial relationship.
The resin material forming the guide body is not especially limited. However, since the contact sliding surface of the guide body with a chain, a belt, or the like functions as a shoe, the material is preferably a so-called xe2x80x9cengineering plastic,xe2x80x9d such as a polyamide type resin having high wear resistance and good lubricating properties. A fiber-reinforced resin may be used for the entire guide body, or may be used concurrently another plastic material. The material of the reinforcing plate is also not especially limited, but the reinforcing plate must have sufficient bending rigidity and strength to function effectively as a reinforcement for the plastic movable guide. Iron-based metals such as cast iron, stainless steel and the like, nonferrous metals such as aluminum, magnesium, titanium and the like, engineering plastics such as polyamide type resin and the like, and fiber reinforced plastics are preferably used as materials for the reinforcing plate.
The plastic movable transmission guide according to the invention, having the above-described configuration, exhibits the following unique effects.
First, because the diameter of the through hole bored in the reinforcing plate is larger than that of the mounting hole of the guide body, the through hole and the mounting hole may be fastened together on a shaft such as a mounting bolt or the like. When the guide is mounted on the shaft, the shaft is engaged with the inner surfaces of a pair of opposed parts of the mounting hole of the guide body, but does not contact the inner periphery of the through hole bored in the reinforcing plate. Therefore, the occurrence of objectionable metallic noise and wear of the reinforcing plate are avoided. Further, since the shaft support means is supported by the inner walls of parts of the mounting hole on both sides of the reinforcing plate, transverse vibration is significantly reduced.
If the through hole bored in the reinforcing plate and the mounting hole bored in the guide body are positioned and locked so that they are on the same axis, even if the guide is subjected to excessive vibration, deformation of the reinforcing plate is prevented, and contact of the inner periphery of the through hole with the supporting shaft can be reliably avoided.